program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  n, k, i, g, b, c, e : integer;
begin
  read (n, k);
  readln;
  if (n>=k) then
  begin
    b:=1;
    for i:=0 to n-1 do
      b:=b*(i+1);
    c:=1;
    for i := 0 to k-1 do
      c:=c*(i+1);
    g:=1;
    for i:=0 to n-k-1 do
      g:=g*(i+1);
  e:=b div (c*g);
  writeln(e);
  end;
  if (n<k) then
    writeln('Error!');
  readln;
end.
 